Estimation of the number of nucleotide sequences in mouse DNA complementary to messenger RNAs specifying a complete mouse immunoglobulin.

A fraction of ribonucleic acid (RNA) enriched in messenger RNA (mRNA) coding for immunoglobulin G (IgG) was isolated from cells of mouse myeloma RPC5 using specifically purified antibodies to immunoprecipitate polyribosomes engaged in IgG psi heavy and K light chain synthesis. More than 85% of the RNA present consisted of IgG mRNA as determined by an analysis of the products translated in its presence in the wheat germ system. IgG mRNA labeled with 125I was hybridized with mouse liver DNA. Approximately 95% of the RNA hybridized with mouse a Cot 1/2 of 4.0 X 103, indicating that the complementary DNA sequences were present less than five times per haploid genome. In contrast, approximately 75% of poly(adenylic acid) containing RNA prepared from unfractionated polyribosomes of RPC5 cells hybridized with a Cot 1/2 of 3.3 X 103; 25% of such RNA formed hybrids at lower Cot values.